McDonalds sent out emails stating that on Jan 15, most of their WiFi spots (currently NOT free) will be switching to Free:

Dear Sir or Madam,
Currently right now McDonalds is a pay per connection unless you have one of our premier accounts or AT&T DSL at your home. Most McDonalds on the 15th will convert to free Wi-Fi, and the login page will be different than what it is now.

Free Internet access will be available at 11,000 of the company's 13,000 U.S. locations, making McDonald's an even friendlier spot for Road Warriors in need of connectivity.
more info:
McDonald's to Offer Free Wi-Fi Internet Access - PC World Business Center